be involved in this. it isn't just about saying fbi will go get them. people before an attack, after an attack, the public has a huge role to play in helping them find someone and being resilient after. >> the definition of social media. michael leiter, thank you for your reporting all day. as we said it's been a day of rapidly moving developments. as investigators continue to do their work, doctors continue to do theirs in boston. after saving so many lives, after dealing, remember, with what looked like combat injuries, some victims are now leaving the hospital telling their stories for the first time. nbc's anne thompson with us tonight from boston with that angle of the story. anne, good evening. >> reporter: good evening, brian. tonight the city of boston is preparing for the arrival of president obama who will attend an interfaith service tomorrow and preparing for what many know will be a long, difficult journey to recovery. in boston, vows of resolve today amid emotions that are still raw. a relieved 20-year-old sarah gerard left the hospital with her leg in a cast.